12A in jet boat, torque at 4000rpm?
 

I've got a 12A motor I would like to use for my 16ft jet boat project.
The Berkeley Jet in the boat would work best at 4000rpm at 200hp,
which translates into 262 lb/ft of torque. I could gear the output
so the engine would run 8000rpm, and thus only need 130 ft/lb of torque.

I think a turbo is probably best just for the noise reduction.
Or can I achieve this 200hp with just a PP port and big carbs?

I'd apprecate any suggestions, need to get this boat running asap,
really want to use the 12A.
Note this is a very low budget project, can't spend much cash.

Thanks, JackB

Low budget but you can afford P-Ports and a big carb?

What's your definition of low budget?

I can afford DIY, looks like PP isn't so difficult, might even have a 600 holley still somewhere. I have lathe, drill press, mig and tig welder, etc etc. I do all my own work. My parts store is CL and the junkyard. ;)
Done plenty of other engines,
made my own 506ci BBF using custom parts, turbo'd a 200ci I6, fuel injected my tractor with my own micro/software. ;)

Just could use some advice, never built a rotary before.
I live the PP idea just looks cool.
Low rpm power or even good idle isn't important for a jet boat,
the jet acts like a 5000rpm stall converter in an automatic.

262ft-lb at 4000 is a bit much for constant duty application, but maybe doable with adequate cooling and a turbo sized more for kindness to the engine rather than good response. (BIG hotside and efficient compressor for that pressure ratio/flow) Response shouldn't really be an issue for a constant-speed kind of application, I'd think.

I wonder if a bridge port with stock-like intake closing would work well for that application. Big ports make more, not less, low-end and midrange power, they just suffer at low *loadings* (think of the power output in a 3D graph) and they really start to scream at the top end, thus the "no low end" fallacy.

12As do not like to run over 6000 for extended periods of time with the stock apex seals. They start to bounce and chatter around that point. Rotor housings and the apex slots suffer, and then you break a seal from the hammering.

I'm going to put a 13b in a jetski. going for a semi p-port setup that opens up at ~5k rpm. to fit in the jetski it's going to need all new intake and exhaust maniffolds, custom made stuff, so i might as well go p-ports for the extra punch. Define's 20b semi pp setup is my model, with some tweaks.

Stock TII turbo will work quite well for 200 hp at low rpm.

A jet boat can cool the engine quite well, engine running too cold more common problem, so should be good here.

I have two turbos from a twin turbo Supra (bought for $100, in good shape, guy just converted to single turbo) might be a bit small if I only use one, the whole twin sequential setup is heavy and complicated. I could try to find another bigger turbo if needed.

I tore into my 12a last night, and found the rear housing was pretty bad.
A guy here had one for sale, so hope to get a good one and put it back together.
I noticed they say to keep the apex seals back in the same place, I did not keep track of them, am I screwed? Is this like a cylinder wall, do you 'hone' the surfaces or just leave them alone?

It isn't in my budget, but with a PP, you could eliminate the center iron, just have a single dual-sided plate for both rotors, would shrink and lighten up the engine a pretty substantial amount.

Oh my.

:scratch::scratch::scratch:

hahaha, it COULD be possible, but completely improbable, and very costly, and in-effective at any thing, you'd want as much intake as possible, use side ports and pports, guess you havent done enough reading.

at the using twin turbos from a supra comment, i'm out of this thread. a carb'd rx8 engine makes the most since for this setup. but no one's done that.

Sure it could be done but unless the person could do ALL the machining necessary (like John Huijben!) on their own the cost would be absolutely prohibitive...unless of course they had bottomless pockets. :lol: The OP mentioned keeping costs down.

A single rotor engine uses custom e-shaft, this engine is built to save as many lbs as possible, usually for airplanes. You could save a lot with this mod, yet still have two rotors, more reliable than a single rotor.

Let's see, $25k for four rotor engines? :confused:

Let's see, you've offered no advice whatsoever. You won't be missed.

the supra turbo is probably too complex/small, but for 4000rpm at a constant speed you probably wont need a giant turbo.

might as well run a lake to air intercooler too.

um if your housing was bad, the seals are too. would you reuse a piston ring from a scored cylinder?

Hi thanks for the input, I will try one supra turbo. I could use two as simple twin (not sequential) adds a lot of weight, I'm trying to make this boat simple and a lot lighter (why I'm converting it to use a jet and the rotary)

I would always replace piston rings. So I need to replace the apex seals?
What about the side seals? The sides are in good shape.

Given I am building my own EFI for this engine, I'm thinking of using E85, so maybe the intercooler isn't needed. Problem is E85 is not available at fuel docks (that I have ever seen) so I could make it use either, but if must run E10 why bother with E85?
I'm also going to eliminate the distributer and run a custom COP just on the leading plugs, I could dial the spark advance with a knob.

i wouldn't use supra parts for anything but a boat anchor....

yea you should change the apex seals, they are the piston rings. side seals you can check the clearance, and replace as needed.

imo, if you have really good temp control you don't need E85. for an intercooler, just buy a smallish one, and stick it in the water.

i'm kind of thinking a stock T2 turbo might actually be about right

Lol!

Shortening a 2 rotor by using just a thin plate would also require a special extra-short eccentric shaft as well as shorter tension bolts, and you'd also need full-length dowel pins since they wouldn't have anything to anchor to in the middle.

I suspect that heat management would be a major issue as well. The end housings have coolant running through them to cool the sides, the center housing does not but it does see a fairly large amount of oil spray from the rotors and I'm all but certain that it is oil cooled. Asking a solid plate to handle the friction of rotors on either side of it as well as the heat loads from combustion... I don't think it'd last very long at all.

I picked up another 12a engine. This one has some mods. The rotor housing are excellent, and the rotors are already nice and clean. Also has a RB lightweight flywheel, and I got a header flange too to fab my turbo exhaust. Yeah. No e-shaft though, so can't go trying to machine a shorter one for a center iron delete motor. :)

The center iron from this motor has been ported, he didn't get to the end plates but has them all marked up for where to grind. I will try to get pics up, but here is my latest idea, to just use the primary intake port, and block off the outer secondaries.
This way I can use a much smaller lighter custom intake manifold.
Given I have a turbo(s), seems to me the motor is not limited by intake port flow,
but boost limits.

I was looking for a T2 motor for a few years, never found one cheap ever.

It might actually work better to use this flat plate idea to build a short four rotor motor..that would make the time and effort a little more worthwhile. Would be great for my boat too, then no turbo/intercooler needed. :)

Took a look at all the parts of the latest 12A, and it must be a very early?
It has what looks like 6mm apex seals, and double side seals.

It came with carbon apex seals which are in excellent shape,
so I'm wondering if I should use these rotors? I've read carbon seals are not so good for turbos. I'm I going to have a balance issue if I use these rotors with the later e-shaft? It looks like all e-shafts are the same, so I'd guess not.
There was a broken round oil ring, maybe that is why it was torn apart.
The front iron was ported, just the rear iron not ported.
Here are the pics, including my bad housing.

The housings look pretty good, from what I can see. Some minor flaking is OK on the edges. Any scratches or chatter wear?

not that I notice, look pretty smooth. So from what I've been reading, the early housings did not have as tough a surface, so they used the carbon apex seals,
later they used harder housing surfaces and could go with the smaller cast iron seals. So if this is correct, then i will need to use the carbon seals with these early housings, otherwise the cast iron seals will wear them out quickly.
The carbon seals wear out, not the housings. Given that 12a housings are NLA, me thinks it best to use the carbon seals because they can be replaced, whereas good housing difficult to find. Also like the idea of not having to buy new apex seals.

My boat is not really used very much, maybe 5-10 times a year, so engine doesn't really need to last very long. But it does get worked hard when it is used.

the early engines do need carbon seals, you should take your later rotors and stat gears and stuff em in the early engine and with the 3mm carbons and just have fun